1. Field of the Invention
This invention relates to a device for scanning a beam spot.
2. Description of the Prior Art
Apparatus for scanning a laser beam spot have heretofore comprised a rotational polygon mirror for deflecting the laser beam and an f-.theta. lens or the like for condensing the deflected beam into a spot moving at a linear speed. In these prior art apparatus, however, the various operating portions have been separate and independent and a predetermined light path interval has been required therebetween and therefore, precise adjustment during the assembly of the apparatus has been very complicated and the assembled apparatus has been bulky.
There are also known apparatus which use an acoustic optical deflector instead of a rotational polygon mirror to make the apparatus compact. An example of such apparatus is disclosed in U.S. Pat. No. 3,514,534, but even in that example, various operating portions are still independent and therefore, cumbersome adjustment has been required during the assembly and the compactness of the apparatus has been limited.
On the other hand, to reproduce images from a magnetic recording medium on which, for example, TV signals are recorded, it is necessary to move the recording medium and a signal reading head relative to each other at a high speed to thereby effectly scanning in order to obtain a high frequency of 4.2 MHz which is the band of NTSC signal. In the conventional VTR for domestic use, mechanical scanning devices which effect reading by a head rotated at a high speed inside of a recording medium wound on a cylinder have been typical. Generally, however, mechanical scanning devices are inferior to optical scanning devices in accuracy and durability in the case of high-speed scanning and accordingly, there have been desired compact recording or reproducing apparatus utilizing an optical scanning device which can readily realize stable high-speed scanning. Recently, attention has particularly been paid to a system which utilizes the magnetic Kerr effect or the Faraday effect to effect beam spot scanning on a magnetic recording medium and thereby accomplish magnetic recording or reproduction. However, the aforementioned disadvantages of the conventional optical scanning devices have prevented their application to compact and high frequency band recording or reproducing apparatus.